Prayers (Salat)
Bukhari :: Book 1 :: Volume 8 :: Hadith 464
Narrated 'Abbad bin Tamim:
that his uncle said, "I saw Allah's Apostle lying flat (on his back) in the mosque with one leg on the other." Narrated Said bin Al-Musaiyab that 'Umar and 'Uthman used to do the same.